Pros
The people and the culture are top of the line at Riot. You are constantly surrounded by the the smartest people in the room and, in general, everyone is moving in the same direction. Culturally this place is intense you have to be a true believer in the company and it's mission in order to get along. But it is precisely that culture that allows Riot to continue to grow and create the right products for players.
Cons
Riot doesn't do things by half measure. The work-life here is intense and the expectations are intense. It is very common to be working 10+ hours every day. There is nothing that requires you to put in that time, but when you are in a company full of competitive people the level of effort never slacks off. Burn out is common, illness rips through the company, and if you begin to lose faith in the culture it's a quick spiral out of the company. In some categories the company also underpays compared to others. The mitigating factor here are the perks like free lunch and open PTO.